1. Field of the Invention
The present invention provides an auto-compensating mechanism (ACM). More specifically, the present invention provides an auto-compensating mechanism having a spring clutch coupling the auto-compensating mechanism housing and a drive shaft and which transfers reverse pick motor torque from the drive shaft to the ACM to rotate the auto-compensating mechanism housing and pick tire away from engagement with a media stack.
2. Description of the Related Art
It has been previously suggested to utilize a tray or bin in order to support a stack of sheets of print media in which the upper most sheet of the stack may be advanced to a processing station or printing area for printing by a laser printer or inkjet printer, for example. In typical printing or duplicating devices, individual sheets of print media are advanced to the processing station by utilizing a paper picking device.
With paper picking devices a critical relationship exists between the pick roller and the media stack. More specifically the relationship involves a normal force between the pick roller and the paper stack. When too much normal force exists, multi-feeds may occur resulting in paper jams. When too little normal force exists, paper will not feed into the printing area. Current devices utilize either a spring loaded paper stack or spring loaded pick roll in order to provide the normal force for picking. Despite extensive tuning of this normal force, usually only a very narrow range of media will run reliably on these devices. In other words, these systems are critically effected by various media characteristics including, but not limited to, density, net weight, stiffness and smoothness of the media surface. Feeding of print media sheets from a stack has been significantly improved by an auto-compensating mechanism (ACM) shown and described in U.S. Pat. No. 5,527,026, issued to Padget et al., which is incorporated by reference herein.
Auto-compensating paper feeders address prior art issues in paper feeding. In an auto-compensating paper feed mechanism or swing-arm designs, the pick roller or tire and media stack are not spring loaded against one another. Instead the pick roll is mounted on the rotating swing arm and the pick roll rests on the media stack. When the pick roll drive is initiated through a gear located on the pivot shaft with the swing arm, a torque is applied to the swing-arm through a gear transmission which rotates the swing arm and pick roll into the paper stack. This generates a normal force which is dictated by the buckling resistance of the media being picked. The normal force is no more than is required to buckle a single sheet of media plus the friction resistance between the first and second sheets. When the upper most sheet has moved, the normal force automatically relaxes and, thus, the auto-compensating mechanism delivers the normal force that what is required to feed a single sheet of media.
According to one design of an auto-compensating mechanism, the ACM may utilize a clutch to allow the tire or pick roller to rotate freely once the print media is indexed in a paper feed direction through, for example, the print area. Although the tire maintains contact with the media and friction is reduced between the pick roller and upper most media sheet, this design still introduces drag on the media which may result in skewing and print defects.
Given the foregoing deficiencies, it will be appreciated that an apparatus is needed which inhibits contact between the auto-compensating mechanism and media stack as a media sheet is advanced by at least one feed roller.